I run the Facebook messenger app on both my Samsung Galaxy S6 (android) and Apple iPhone 4S (iOS). However when sending a message to someone who isn't using Facebook messenger the S6 always says 'seen' even when the person is inactive. When I check the iPhone it correctly says 'sent'. Why are the two apps giving different delivery statuses and how can I fix this?
Added (1). It seems to work correctly on both devices when sending messages to those on Facebook messenger.
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Why do my Facebook Messenger apps give different delivery statuses?